Nickel active material precursor for lithium secondary battery, method for producing nickel active material precursor, nickel active material for lithium secondary battery produced by method, and lithium secondary battery having cathode containing nickel active material

ABSTRACT

Provided are a nickel-based active material precursor for a lithium secondary battery including a core, an intermediate layer located on the core, and a shell located on the intermediate layer, wherein porosity gradually decreases in the order of the core, the intermediate layer, and the shell, and each of the intermediate layer and the shell has a radial arrangement structure, a method for producing the nickel-based active material precursor, a nickel-based active material produced therefrom, and a lithium secondary battery including a cathode containing the nickel-based active material.

TECHNICAL FIELD

The present disclosure relates to nickel-based active materialprecursors for lithium secondary batteries, methods for producing thesame, nickel-based active materials for lithium secondary batteriesproduced therefrom, and lithium secondary batteries including cathodescontaining the nickel-based active materials.

BACKGROUND ART

With the development of portable electronic devices, communicationdevices, and the like, there is an increasing demand for lithiumsecondary batteries having high energy density.

Lithium nickel manganese cobalt composite oxides, lithium cobalt oxides,and the like have been used as cathode active materials of lithiumsecondary batteries. However, when such a cathode active materials areused, cracks occur in primary particle units with repeated charging anddischarging, thereby reducing the long lifespan of a lithium secondarybattery, increasing battery resistance, and failing to satisfy desiredbattery capacity characteristics. Therefore, there is a need to improvethese characteristics.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided is a nickel-based active material precursor for a lithiumsecondary battery having an increased lithium ion utilization rate.

Provided is a method of producing the nickel-based active materialprecursor.

Provided is a nickel-based active material obtained from thenickel-based active material precursor and a lithium secondary batteryincluding a cathode containing the nickel-based active material.

Solution to Problem

According to an aspect of the present disclosure, a nickel-based activematerial precursor for a lithium secondary battery includes a core, anintermediate layer located on the core, and a shell located on theintermediate layer, wherein porosity gradually decreases in the order ofthe core, the intermediate layer, and the shell, and each of theintermediate layer and the shell has a radial arrangement structure.

According to another aspect of the present disclosure, a method ofproducing a nickel-based active material precursor for a lithiumsecondary battery includes a first process of forming a core of thenickel-based active material precursor by reacting a complexing agent, apH regulator, and a metal raw material for forming the nickel-basedactive material precursor, a second process of forming an intermediatelayer on the core obtained in the first process, and a third process offorming a shell on the intermediate layer obtained in the secondprocess, wherein stirring powers of the second process and the thirdprocess are lower than that of the first process.

The pH levels of reaction mixtures of the first process, the secondprocess, and the third process are the same, and concentrations of thecomplexing agent gradually increase in the order of the first process,the second process, and the third process.

According to another aspect of the present disclosure, a lithiumsecondary battery includes a cathode containing the nickel-based activematerial for a lithium secondary battery.

Advantageous Effects of Disclosure

A nickel-based active material precursor for a lithium secondary batteryaccording to an example embodiment has a density gradient from a core toa shell, and thus resistance to lithium diffusion is reduced. By using acathode including a nickel-based active material obtained from thenickel-based active material precursor, a lithium secondary batteryhaving increased discharge capacity and improved charge/dischargeefficiency may be manufactured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A schematically illustrates a structure of a nickel-based activematerial precursor according to an example embodiment.

FIG. 1B is a schematic diagram illustrating shapes of plate particles.

FIG. 1C is a diagram for describing the definition of a radialarrangement in a secondary particle of a nickel-based active materialaccording to an example embodiment.

FIG. 2 schematically illustrates a structure of a lithium secondarybattery according to an example embodiment.

FIGS. 3 and 4 are scanning electron microscope images showing states ofcathodes of coin half-cells prepared according to Manufacture Examples 1and 2 and Comparative Example 1 after evaluation of lifespancharacteristics at high temperature.

REFERENCE NUMERALS

10: Core 11: Intermediate layer 12: Shell 21: Lithium secondary battery22: negative electrode 23: Positive electrode 24: Separator 25: Batterycase 26: Cap assembly

MODE OF DISCLOSURE

Hereinafter, a nickel-based active material precursor for a lithiumsecondary battery, a method for producing the same, and a lithiumsecondary battery including a cathode containing the nickel-based activematerial precursor according to the present disclosure will be describedin detail with reference to the accompanying drawings.

Hereinafter, a precursor according to an example embodiment of thepresent disclosure will be described with reference to FIGS. 1A to 1C.FIG. 1A schematically illustrates a structure of a nickel-based activematerial precursor according to an example embodiment. FIG. 1B is aschematic diagram illustrating shapes of plate particles. FIG. 1C is adiagram for describing definition of radial arrangement in a secondaryparticle of a nickel-based active material according to an exampleembodiment.

Referring to FIG. 1A, a nickel-based active material precursor accordingto the embodiment has a structure in which a core 10, an intermediatelayer 11, and a shell 12 are sequentially stacked. Porosity graduallydecreases from the core 10 toward the shell 12, and density graduallyincreases in the order of the core 10, the intermediate layer 11, andthe shell 12. The nickel-based active material precursor according tothe embodiment has porosity gradually decreasing from an inner portionto an outer portion. Thus, when an active material is prepared using theprecursor, stress generated by volume changes caused during charging anddischarging may be absorbed by the inside and breakage of the activematerial is reduced, thereby improving a lifespan of a battery.

Throughout the specification, the term “porosity” refers to a ratio ofan area occupied by pores to a total area.

Because the nickel-based active material precursor according to theembodiment has a density gradient, a surface area where diffusion oflithium occurs increases and diffusion of lithium is facilitated. Inaddition, because open pores are well developed on the surface, anelectrolyte may easily permeate therethrough facilitating diffusion oflithium. Also, because the core of the nickel-based active materialprecursor has a radial arrangement structure, stress may be reducedduring charging and discharging. The core 10 may occupy an area a of 65to 85% in length from the center based on a total length from the centerto the surface. For example, the core 10 may have an area other than anarea within 2 μm in thickness from the outermost boundary of thenickel-based active material precursor.

The core 10 may have a porosity of 15 to 20%. A pores size of the core10 may be greater than that of the shell 12 and may be in a range of 150nm to 1 μm, for example, 150 nm to 550 nm, for example, 200 nm to 500nm. When the pore size of the core of the secondary particles is greaterthan that of the shell, a lithium diffusion distance is shorter thanthat of core where the pore size is equal to the pore size of the shelland the pores may reduce volume changes caused during charging anddischarging without being exposed to an electrolytic solution.Throughout the specification, the term “pore size” refers to an averagediameter of pores when the pores are spherical or circular. When thepore has an oval shape, or the like, the pore size refers to an averagelength of a major axis of the pore.

The core 10 may have an irregular porous structure. The term “irregularporous structure” refers to a structure including pores with irregularor non-uniform sizes and shapes. The core 10 may include plate particleswhich may irregularly be arranged. Referring to FIG. 1B, a plateparticle may have a polygonal nanoplate shape such as a hexagonal plateshape (A), a nanodisc shape (B), and a rectangular parallelepiped shape(C). The term “plate particle” refers to a particle having a thicknesssmaller than a length of a major axis (a plane direction). The length ofthe major axis refers to a maximum length of the widest plane of theplate particle. That is, in FIG. 1B, a thickness t of the plate particleis smaller than lengths a and b in the plane direction. The length a inthe plane direction may be the same as or greater than the length b inthe plane direction. A direction in which the thickness t of the plateparticle is defined is referred to as a thickness direction, and adirection including the lengths a and b is referred to as a planedirection. The plate particle has an average length of 150 to 500 nm,for example, 200 to 380 nm, particularly, 290 to 360 nm. The averagelength refers to an average of a major axial length and a minor axallength of the plate particle in the plane direction. The averagethickness of the plate particle is in a range of 100 to 200 nm, forexample 120 to 180 nm, particularly 130 to 150 nm. In addition, a ratioof the average thickness to the average length is in a range of 1:2 to1:5, for example 1:2.1 to 1:5, particularly 1:2.3 to 1:2.9. When theaverage length, the average thickness, and the ratio of the averagethickness to the average length satisfy the above-described ranges,relatively many lithium diffusion paths are formed between grainboundaries of particles and many crystal planes enabling transfer oflithium to the shell are exposed on the surface, and thus a degree oflithium diffusion increases, thereby improving initial efficiency andcapacity.

The major axis of the plate particle may be arranged in a radialdirection. In this case, a crystal plane (plane perpendicular to crystalplane (001)) through which lithium passes is exposed on the surface of asecondary particle. As used herein, the term “radial(ly)” as used hereinmeans that a direction of the thickness t of a plate may be arranged ina direction perpendicular to or within ±5° of a direction perpendicularto a direction R toward a center of the secondary particle as shown inFIG. 1C. When primary particles are radially arranged, the pores exposedon surfaces therebetween may be toward a central direction, therebyfacilitating lithium diffusion from the surfaces. Upon deintercalationof lithium, pores may be present near a (001) crystal plane direction,i.e., a direction in which particles may expand, such that bufferingaction is enabled. Since the size of each of plate primary particles issmall, cracks may be less likely to be formed upon shrinkage andexpansion. The internal pores of the core may additionally easevolumetric change, and thus cracks between the primary particles may beless likely to be formed upon charge/discharge, thereby improvinglifespan characteristics and reducing an increase in resistance.

The shell (outer) 12 refers to an area b of 5 to 15% by length from theoutermost surface or an area within 2 μm from the outermost surface ofthe nickel-based active material precursor, based on a total distancefrom the center to the surface of the nickel-based active materialprecursor as shown in FIG. 1A.

The shell 12 has a porosity of, for example, 2% or less, for example,0.1 to 2%. The shell 12 may have a pore size of less than 150 nm, forexample, 100 nm or less, for example, 20 to 90 nm. The shell 12 mayinclude plate particles like the core 10 as described above, and theplate particles may have a radial arrangement.

The intermediate layer 11 is an area c other than the core 10 and theshell 12. The intermediate layer 11 may have a porosity of 10 to 15%.

The nickel-based active material precursor according to the embodimentmay have a specific surface area of 4 to 10 m²/g. Due to such a largespecific surface area of the nickel-based active material precursor,diffusion of lithium may be performed more easily.

The nickel-based active material precursor according to the embodimentis a compound represented by Formula 1 below.

Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)(OH)₂

In Formula 1, M is an element selected from the group consisting ofboron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba),titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu),zirconium (Zr), and aluminum (Al), and x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1,0≤y<1, and 0≤z<1 are satisfied. In Formula 1, 0<x≤0.33, 0≤y≤0.5,0≤z≤0.05, and 0.33≤(1-x-y-z)≤0.95 are satisfied. According to anotherexample embodiment, 0≤z≤0.05, 0<x≤0.33, and 0≤y≤0.33 are satisfied inFormula 1. According to an example embodiment, z is 0 in Formula 1.According to another example embodiment, when 0<z≤0.05 is satisfied inFormula 1, M may be aluminum. A metal hydroxide of Formula 1 may be, forexample, Ni_(0.6)Co_(0.2)Mn_(0.2)(OH)₂, Ni_(0.5)Co_(0.2)Mn_(0.3)(OH)₂,Ni_(0.33)Co_(0.33)Mn_(0.33)(OH)₂, or Ni_(0.8)Co_(0.1)Mn_(0.1)(OH)₂.

A size of the nickel-based active material precursor according to theembodiment is in a range of 5 to 25 μm. When the size of the secondaryparticle of the nickel-based active material precursor is within thisrange, lithium ions may easily be used.

Hereinafter, a method of producing a nickel-based active materialprecursor according to an embodiment will be described.

The nickel-based active material precursor is prepared to have excellentstructural stability by appropriately maintaining pores formed by thecrystal planes (001) while minimizing exposure of the crystal planes(001). In addition, the center of the nickel-based active materialprecursor has a radial arrangement structure and the length of lithiumdiffusion is efficiently controlled by this structure.

The method of producing the nickel-based active material precursoraccording to an embodiment may be divided into a first process, a secondprocess, and a third process according structure-forming processes forthe core, the intermediate layer, and the shell. In the first process,the second process, and the third process, processing conditions such asconcentration and amount of a metal raw material and concentration andamount of ammonia water as a complexing agent may vary.

In the first process, a complexing agent, a pH regulator, and a metalraw material forming a nickel-based active material precursor are mixedand reacted to form a core of the nickel-based active materialprecursor. According to an embodiment, the first process is performed byadding the complexing agent and the pH regulator to a reactor and thenadding the metal raw material thereto to perform the reaction. When thepH of the reaction mixture is changed as the reaction proceeds, the pHregulator may further be added thereto, if required, to adjust the pH ofthe reaction mixture within a predetermined range.

Subsequently, the second process is performed to form the intermediatelayer on the core obtained in the first process, and then the thirdprocess is performed to form the shell on the intermediate layerobtained in the second process.

Stirring powers of the second process and the third process are reducedwhen compared with a stirring power of the first process. The stirringpowers of the second process and the third process may be the same. Thestirring power of each process is in a range of 0.1 to 6 KW/m², forexample 1 to 3 KW/m².

The pH of each of the first process, the second process, and the thirdprocess is controlled in a range of 10 to 12.

In the above-described method of producing the nickel-based activematerial precursor, the concentration of the complexing agent graduallyincreases in the order of the first process, the second process, and thethird process. The concentration of the complexing agent may be in arange of 0.1 to 0.7 M. As the complexing agent, for example, ammoniawater is used.

In the first process, the core which is the center of the particle isformed by adding the raw material while maintaining the pH of thereaction mixture. In the second process, after maintaining a productobtained from the first process for a predetermined time, the amountsand concentrations of the metal raw material and the complexing agentare increased to prevent a decrease in growth rates of the particlescaused in accordance with the growth of particles.

Subsequently, after maintaining a reaction product obtained from thesecond process for a predetermined time, the amounts and concentrationsof the metal raw material and the complexing agent are increased toprevent a decrease in growth rates of the particles caused in accordancewith the growth of particles. The porosity of internal portion of thenickel-based active material precursor particle is determined accordingto a time of each process described above.

In the nickel-based active material precursor according to anembodiment, the porous core structure is influenced by the amount of themetal raw material, the concentration of the complexing agent, and thepH of the reaction mixture.

The pH regulator serves to form a precipitate from the reaction mixtureby adjusting the pH of the reaction mixture. Examples of the pHregulator are sodium hydroxide (NaOH), sodium carbonate (Na₂CO₃), andsodium oxalate (Na₂C₂O₄). As the pH regulator, for example, sodiumhydroxide (NaOH) is used.

The complexing agent adjusts a reaction rate of forming a precipitate incoprecipitation reaction and may be ammonium hydroxide (NH₄OH) (ammoniawater), citric acid, and the like. The complexing agent may be used inany amount commonly used in the art. As the complexing agent, forexample, ammonia water is used.

The concentration of the complexing agent may be in a range of 0.1 to0.7 M, for example, about 0.2 to about 0.5 M. In addition, theconcentration of the metal raw material is in a range of 0.1 to 0.5 M,for example, 0.3 M.

The amount of the metal raw material may be in a range of 50 to 100ml/min in the first process.

In the first process, the core of the nickel-based active material isformed.

Subsequently, the second process of adding the metal raw material andthe complexing agent to a resultant reaction product of the firstprocess, adjusting the pH of the reaction mixture, and then proceeding areaction of the reaction mixture is performed.

In the second process, the concentration of the complexing agent is in arange of, for example, 0.3 to 1.0 M. In the second process, the amountof the metal raw material is in a range of 90 to 120 ml/min, and theamount of the complexing agent is in a range of 8 to 12 ml/min.

The third process of adding the metal raw material and the complexingagent to a resultant reaction product of the second process, adjustingthe pH of the reaction mixture, and proceeding a reaction of thereaction mixture is performed to prepare the nickel-based activematerial precursor.

In the third process, the concentration of the complexing agent may bein a range of 0.35 to 1.0 M.

The reaction conditions of the third process considerably influence asurface depth of a porous layer of the nickel-based active materialprecursor.

In the third process, the amount of the metal raw material is in a rangeof 120 to 150 ml/min, and the amount of the complexing agent is in arange of 12 to 18 ml/min.

In the preparation process, as the metal raw material, a metal precursoris used in consideration of the composition of the nickel-based activematerial precursor. The metal raw material may be metal carbonate, metalsulfate, metal nitrate, metal chloride, and the like.

To prepare the compound represented by Formula 1, a manganese precursor,a nickel precursor, and a cobalt precursor may be used as the metal rawmaterial. The manganese precursor, the nickel precursor, and the cobaltprecursor may be, for example, manganese sulfate, nickel sulfate, cobaltsulfate, manganese chloride, nickel chloride, and cobalt chloride.

Hereinafter, a method of producing a nickel-based active materialaccording to an embodiment will be described.

A lithium precursor and the nickel-based active material precursoraccording to an embodiment are mixed in a certain molar ratio and thensubjected to a low-temperature heat treatment at 600 to 800° C. toprepare a nickel-based active material.

The lithium precursor may be, for example lithium hydroxide, lithiumfluoride, lithium carbonate, or any mixture thereof. A mixing ratio ofthe lithium precursor and the nickel-based active material precursor isadjusted stoichiometrically to prepare a nickel-based active materialhaving a desired composition.

The mixing may be performed by dry mixing or by using a mixer.

The low-temperature heat treatment is performed in an oxidizing gasatmosphere. The oxidizing gas atmosphere is performed using an oxidizinggas such as oxygen or air, and the oxidizing gas may include, forexample, 10 to 20 vol % of oxygen or air and 80 to 90 vol % of an inertgas.

The heat treatment may be performed at a temperature where reactions ofthe lithium precursor and the nickel-based active material precursorproceed and at a densification temperature or less than a densificationtemperature. In this regard, the densification temperature refers to atemperature at which crystallization is sufficiently performed torealize a charge capacity obtained by an active material.

The heat treatment is performed, for example, at 600 to 800° C., forexample, at 700 to 800° C.

A heat treatment time vary according to the temperature of thelow-temperature heat treatment, or the like, but may be, for example,from 3 to 10 hours.

When the heat treatment is performed under the above-describedconditions, primary particles of a nickel-based active materialincluding a shell having a radial arrangement structure and a corehaving an irregular porous structure may be prepared. An averageparticle diameter of the primary particles of the nickel-based activematerial may be in a range of 100 to 250 nm in a minor axis direction.Due to such an average particle diameter, stress caused by volumechanges during charging and discharging may be suppressed.

Secondary particles of the nickel-based active material may be subjectedto a second heat treatment (high-temperature heat treatment,high-temperature sintering) in an oxidizing gas atmosphere whileinhibiting the gases from being exhausted.

By inhibiting the gases from being exhausted in the preparation of thesecondary particles of the nickel-based active material, the atmosphereinside the reactor may be maintained as much as possible, and thusgeneration of a resistive layer of the secondary particles of thenickel-based active material is inhibited and particle densification maybe performed.

The high-temperature heat treatment is performed, for example, at 700 to900° C. A high-temperature heat treatment time may vary according to thetemperature of the high-temperature heat treatment, and the like, butmay be, for example, in a range of 3 to 10 hours. An average particlediameter of the secondary particles of the nickel-based active materialis in a range of 2 to 18 μm, for example, 3 to 12 μm. In thehigh-temperature heat treatment of the primary particles of thenickel-based active material, a hetero-element compound including atleast one selected from zirconium (Zr), titanium (Ti), aluminum (Al),magnesium (Mg), tungsten (W), phosphorus (P), and boron (B) may furtherbe added thereto.

Examples of the hetero-element compound including at least one selectedfrom zirconium (Zr), titanium (Ti), aluminum (Al), magnesium (Mg),tungsten (W), phosphorus (P), and boron (B) may include titanium oxide,zirconium oxide, aluminum oxide, and the like. The hetero-elementcompound may include both of lithium (Li) and a hetero-element. Thehetero-element compound may be, for example, i) an oxide of at least oneselected from i) zirconium (Zr), titanium (Ti), aluminum (Al), magnesium(Mg), tungsten (W), phosphorus (P), and boron (B) or ii) an oxideincluding lithium and at least one selected from zirconium (Zr),titanium (Ti), aluminum (Al), magnesium (Mg), tungsten (W), phosphorus(P), and boron (B).

The hetero-element compound may be, for example, ZrO₂, Al₂O₃, LiAlO₂,Li₂TiO₃, Li₂ZrO₃, LiBO₃, and Li₃PO₄.

An amount of the compound including the above-described hetero-elementmay be in a range of 0.0005 to 0.01 parts by weight based on 100 partsby weight of the secondary particles of the nickel-based activematerial. The existence and distribution of the oxide including thehetero-element may be identified by Electron Probe Micro-Analysis(EPMA).

According to an example embodiment, the nickel-based active material maybe, for example, a compound represented by Formula 2 below.

Li_(a)(Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z))O₂   Formula 2

In Formula 2, M is an element selected from boron (B), magnesium (Mg),calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V),chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), and 0.95≤a≤1.3, x≤(1-x-y-z), y≤91-x-y-z), 0<x<1, 0≤y<1 and 0≤z<1are satisfied. As described above, in the nickel-based active materialof Formula 1, an amount of Ni is greater than that of Co, and the amountof Ni is greater than that of Mn.

In Formula 2, 0.95≤a≤1.3, for example, 1.0≤a≤1.1, 0<x≤1/3, for example,0.1≤x≤1/3, 0≤y≤0.5, for example, 0.05≤y≤0.3, 0≤z≤0.05, and1/3≤(1-x-y-z)≤0.95 are satisfied. For example, in Formula 2,1/3≤(1-x-y-z)≤0.95 is satisfied.

According to another example embodiment, in Formula 2, 0≤z≤0.05,0<x≤1/3, and 0≤y≤1/3 are satisfied, and z is 0.

According to another example embodiment, when 0<z≤0.05 is satisfied inFormula 2, M may be aluminum.

In the nickel-based active material, the amount of Ni is in a range of1/3 to 0.95 mol %, which is greater than that of each of Mn and Co,based on the total amount of transition metals (Ni, Co, and Mn).

In the nickel-based active material, the amount of Ni is greater thaneach of the other transition metals based on 1 mole of the transitionmetals. By using the nickel-based active material having such a high Nicontent, the degree of lithium diffusion increases, conductivityincreases, and higher capacity may be obtained at the same voltage in alithium secondary battery including a cathode containing thenickel-based active material. However, lifespan characteristics maydeteriorate due to occurrence of cracks.

The nickel-based active material is LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂,LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂, LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂,LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂, or LiNi_(0.85)Co_(0.1)Al_(0.05)O₂.

The overall porosity of the nickel-based active material is in a rangeof 1 to 8%, for example, 1.5 to 7.3%. A porosity of the outer portion ofthe nickel-based active material is less than that of the inner portion.Pores exposed on the surface arranged toward the center, and sizes ofthe pores are 150 nm less, for example, in a range of 10 to 100 nm whenviewed from the surface. The porosity of the inner portion is in a rangeof 2 to 20%, and a closed porosity of the outer portion is in a range of0.1 to 2%. The term “closed porosity” refers to a fraction of closedpores (pores into which an electrolytic solution cannot permeate) withrespect to a total volume of pores.

In the nickel-based active material according to an example embodiment,the porosity of the inner portion (pore fraction) is in a range of 3.3to 16.5% and the porosity of the outer portion (pore fraction) is in arange of 0.3 to 0.7%.

By including radial plate particles, the nickel-based active materialaccording to an example embodiment may assist diffusion of lithium andsuppress stress caused by volume changes during charging anddischarging, thereby inhibiting occurrence of cracks. Also, the radialplate particles may increase an active surface area required for lithiumdiffusion by reducing a surface resistive layer and increasing lithiumdiffusion directions on the surface during the manufacture. In thenickel-based active material according to another example embodiment,the outer portion includes plate particles whose major axes are alignedin a radial direction and the inner portion includes short, flat plateparticles having a length of 150 nm to 200 nm, for example, nanodiscshaped particles.

The nickel-based active material according to an example embodimentincludes radial plate particles and non-radial plate particles. Anamount of the non-radial plate particle may be 20 wt % or less, forexample, in a range of 0.01 to 10 wt %, particularly, 0.1 to 5 wt %,based on 100 parts by weight of a total weight of the radial plateparticles and the non-radial plate particles. When the nickel-basedactive material includes the non-radial particles within the rangesabove in addition to the radial plate particles, diffusion of lithium isefficiently performed and a lithium secondary battery having improvedlifespan characteristics may be manufactured.

In the nickel-based active material according to an example embodiment,the core may have a pore size of 150 nm to 550 μm, and the shell mayhave a pores size of less than 150 nm. The core of the nickel-basedactive material may have closed pores, and the shell may have closedpores and/or open pores. Closed pores are difficult to contain anelectrolyte, whereas open pores may contain the electrolyte in the poresof the core. Throughout the specification, a closed pore refers to anindependent pore having a closed wall structure without being connectedto another pore and an open pore refers to a continuous pore having awall structure, at least one portion of which is open, and connected tothe shell of the particle.

The secondary particle has open pores having a size of less than 150 nmtoward at a central area of the core.

When the active material is discharged, a diffusion rate of lithiumdecreases at the end of discharging and large-sized secondary particlesof the nickel-based active material increase resistance to permeation oflithium into the cores of the secondary particles of the nickel-basedactive material, and thus discharge capacity decreases in comparisonwith charge capacity, thereby deteriorating charge/discharge efficiency.However, in the secondary particle of the nickel-based active materialaccording to an example embodiment, the porous core structure may reducea diffusion distance to the core and the shell radially aligned towardthe surface may facilitate intercalation of lithium into the surface. Inaddition, due to small-sized primary particles of the nickel-basedactive material, lithium transfer paths may be easily secured amongcrystal grains. Also, because the primary particles have small sizes andpores between the primary particles buffer volume changes caused duringcharging and discharging, stress caused by volumes changes duringcharging and discharged may be minimized.

The secondary particle of the nickel-based active material precursoraccording to an example embodiment may have open pores toward the centerof the core with a size of less than 150 nm, for example 25 to 148 nm.The open pore is an exposed pore through which an electrolyte flows.According to an example embodiment, the open pore is formed to a depthof less than 150 nm, for example, 0.001 to 1000 nm, for example 1 to 50nm, on average, from the surface of the secondary particle of thenickel-based active material.

C-planes of the primary particles of the nickel-based active materialaccording to an example embodiment are aligned in the radial direction.

According to another embodiment, a lithium secondary battery including acathode containing the nickel-based active material, an anode, and anelectrolyte interposed therebetween is provided. A method of producingthe lithium secondary battery will be described later.

The lithium secondary battery according to an example embodiment mayfurther include a separator in addition to the electrolyte.

The cathode and the anode are prepared by coating a cathode activematerial layer-forming composition and an anode active materiallayer-forming composition on current collectors and drying the coatedcompositions, respectively.

The cathode active material layer-forming composition is prepared bymixing a cathode active material, a conductive agent, a binder, and asolvent, and the cathode active material according to an exampleembodiment is used as the cathode active material.

The binder, as a component assisting binding of the active material tothe conductive agent and to the current collector, may be added theretoin an amount of 1 to 50 parts by weight based on 100 parts by weight ofa total weight of the cathode active material. Examples of the bindermay include, but are not limited to, polyvinylidene fluoride, polyvinylalcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM),sulfonated EPDM, styrene-butadiene rubber, fluoride rubber, and variouscopolymers. An amount of the binder may be in a range of 2 to 5 parts byweight based on 100 parts by weight of the total weight of the cathodeactive material. When the amount of the binder is within the rangeabove, a high binding force of the active material to the currentcollector is obtained.

The conductive agent may be any material that does not cause anychemical change in a battery and has conductivity, without limitation.For example, the conductive agent may be: graphite such as naturalgraphite and artificial graphite; a carbonaceous material such as carbonblack, acetylene black, ketjen black, channel black, furnace black, lampblack, and thermal black; conductive fiber such as carbon fiber andmetal fiber; carbon fluoride; metal powder such as aluminum powder andnickel powder; conductive whisker such as zinc oxide and potassiumtitanate; conductive metal oxide such as titanium oxide; and conductivematerials such as polyphenylene derivatives.

An amount of the conductive agent may be in a range of 2 to 5 parts byweight based on 100 parts by weight of the total weight of the cathodeactive material. When the amount of the conductive agent is within therange above, a finally obtained electrode has excellent conductivity.

Examples of the solvent may include, but are not limited to,N-methylpyrrolidone.

An amount of the solvent may be in a range of 1 to 10 parts by weightbased on 100 parts by weight of the cathode active material. When theamount of the solvent is within the range above, a process of formingthe active material layer may efficiently be performed.

The cathode current collector may be any material having a thickness of3 to 500 μm and high conductivity and not causing any chemical change ina battery without limitation. Examples of the cathode current collectormay include stainless steel, aluminum, nickel, titanium, heat-treatedcarbon, or aluminum or stainless-steel surface-treated with carbon,nickel, titanium, silver, or the like. The current collector may have asurface on which irregularities are formed to enhance adhesive force ofthe cathode active material and may be used in any of various formsincluding films, sheets, foils, nets, porous structures, foams, andnon-woven fabrics.

Separately, an anode active material, a binder, a conductive agent, anda solvent are mixed to prepare an anode active material layer-formingcomposition

Examples of the anode active material include, but are not limited to, acarbonaceous material such as graphite and carbon, lithium metal, analloy thereof, and a silicon oxide-based material. According to anexample embodiment of the present disclosure, silicon oxide is used.

The binder is added thereto in an amount of 1 to 50 parts by weightbased on 100 parts by weight of a total weight of the anode activematerial. The binder may be the same type as that of the cathode,without limitation.

The conductive agent is used in an amount of 1 to 5 parts by weightbased on 100 parts by weight of the total weight of the anode activematerial. When the amount of the conductive agent is within this range,a finally obtained electrode has excellent conductivity.

The solvent is used in an amount of 1 to 10 parts by weight based on 100parts by weight of the total weight of the anode active material. Whenthe amount of the solvent is within this range, a process of forming ananode active material layer is easily performed.

The conductive agent and the solvent may be the same types as those usedin preparing the cathode.

The anode current collector is generally formed to have a thickness of 3to 500 μm. The anode current collector may be any conductive materialnot causing any chemical change in a battery without limitation.Examples of the anode current collector may include, but are not limitedto, copper, stainless steel, aluminum, nickel, titanium, heat-treatedcarbon, copper or stainless-steel surface-treated with carbon, nickel,titanium, silver, or the like, or an aluminum-cadmium alloy. Inaddition, like the cathode current collector, the anode currentcollector may have a surface on which irregularities are formed toenhance adhesive force of the anode active material and may be used inany of various forms including films, sheets, foils, nets, porousstructures, foams, and non-woven fabrics.

The separator is interposed between the cathode and the anode eachprepared according to the above-described process.

The separator may have a pore diameter of 0.01 to 10 μm and a thicknessof 5 to 300 μm. Particularly, examples of the separator include: anolefin-based polymer such as polypropylene and polyethylene; or a sheetor non-woven fabric formed of glass fibers. When a solid electrolytesuch as a polymer is used as the electrolyte, the solid electrolyte mayalso serve as a separator.

A lithium salt-containing non-aqueous electrolyte is formed of anon-aqueous electrolytic solution and lithium. A non-aqueous electrolytemay be a non-aqueous electrolytic solution, an organic solidelectrolyte, an inorganic electrolyte, and the like.

Examples of the non-aqueous electrolytic solution may include, but arenot limited to, any aprotic organic solvent such as N-methylpyrrolidinone, propylene carbonate, ethylene carbonate, butylenecarbonate, dimethyl carbonate, diethyl carbonate, gamma-butyro lactone,1,2-dimethoxy ethane, 2-methyl tetrahydrofuran, dimethylsulfoxide,1,3-dioxolane, N,N-formamide, N,N-dimethylformamide, dioxolane,acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoricacid triester, trimethoxy methane, dioxolane derivatives, sulfolane,methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonatederivatives, tetrahydrofuran derivatives, ether, methyl propionate, andethyl propionate.

Examples of the organic solid electrolyte include, but are not limitedto, polyethylene derivatives, polyethylene oxide derivatives,polypropylene oxide derivatives, phosphoric acid ester polymers,polyvinyl alcohol, and polyvinylidene fluoride.

Examples of the inorganic solid electrolyte include, but are not limitedto, Li₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄-Lil-LiOH, and Li₃PO₄—Li₂S—SiS₂.

The lithium salt may be a material easily dissolved in the non-aqueouselectrolyte, for example, but is not limited to, LiCl, LiBr, Lil,LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆,LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi, (FSO₂)₂NLi, lithiumchloroborate, lower aliphatic lithium carboxylate, and lithiumtetraphenyl borate.

FIG. 2 is a cross-sectional view schematically illustrating arepresentative structure of a lithium secondary battery according to anembodiment.

Referring to FIG. 2, a lithium secondary battery 21 includes a cathode23, an anode 22, and a separator 24. The cathode 23, the anode 22, andthe separator 24 are wound or folded, and then accommodated in a batterycase 25. Subsequently, an organic electrolyte is injected into thebattery case 25, and the battery case 25 is sealed with a cap assembly26, thereby completing the manufacture of the lithium secondary battery21. The battery case 25 may have a cylindrical, rectangular, orthin-film shape. For example, the lithium secondary battery 21 may be alarge-sized thin-film battery. The lithium secondary battery may be alithium ion battery. The separator is interposed between the cathode andthe anode to form a battery assembly. After the battery assembly isstacked in a bi-cell structure and impregnated with the organicelectrolyte, the obtained resultant is accommodated in a pouch, therebycompleting the manufacture of a lithium ion polymer battery. Inaddition, a plurality of battery assemblies may be stacked to form abattery pack, which may be used in any device that requires highcapacity and high output. For example, the battery pack may be used innotebook computers, smart phones, and electric vehicles.

Also, the lithium secondary battery may be used in electric vehicles(EVs) due to excellent storage stability at high temperature, lifespancharacteristics, and high-rate characteristics. For example, the lithiumsecondary battery may be used in hybrid vehicles such as plug-in hybridelectric vehicles (PHEVs).

Hereinafter, the present disclosure will be described in more detailwith reference to the following examples and comparative examples.However, the following examples and comparative examples are merelypresented to exemplify the present disclosure, and the scope of thepresent disclosure is not limited thereto.

In the following examples, NH₃ is ammonia water.

EXAMPLE 1

A nickel-based active material precursor (Ni_(0.6)Co_(0.2)Mn_(0.2)OH)was synthesized according to a co-precipitation method described below.As a metal raw material forming the nickel-based active materialprecursor in the following manufacturing process, nickel sulfate, cobaltsulfate, and manganese sulfate were used.

[First process: 1.5 kW/m³, 0.30 M of NH₃, pH of 10 to 11, and reactiontime of 6 hours]

First, ammonia water having a concentration of 0.30 M was added to areactor. Reaction was initiated while adding a metal raw material and acomplexing agent at respective speeds of 90 ml/min and 10 ml/min at astirring power of 1.5 kW/m³ at a reaction temperature of 50° C.

The reaction was continued for 6 hours while adding NaOH thereto tomaintain the pH. After identifying that an average particle size of thecore particle obtained as a result of the reaction was in a range ofabout 5.5 to about 6.5 μm, a second process was carried out as follows.

[Second process: 1.0 kW/m³, 0.35 M of NH₃, pH of 10 to 11, and reactiontime of 6 hours]

The metal raw material and the complexing agent were added to thereactor at respective speeds of 100 ml/min and 15 ml/min whilemaintaining the reaction temperature of 50° C. such that theconcentration of the complexing agent was maintained at 0.35 M. Thereaction was continued for 6 hours while adding NaOH thereto to maintainthe pH. In this case, the stirring power was 1.0 kW/m³ which was lowerthan that of the first process. After identifying that an averageparticle size of a product including the core and an intermediate layerobtained as a result of the reaction was in a range of about 9 to about10 μm, a third process was carried out as follows.

[Third process: 1.0 kW/m³, 0.40 M of NH₃, pH of 10 to 11, and reactiontime of 4 hours]

The metal raw material and the complexing agent were added to thereactor at respective speeds of 150 ml/min and 20 ml/min whilemaintaining the reaction temperature of 50° C. such that theconcentration of the complexing agent was maintained at 0.40 M. Thereaction was continued for 4 hours while adding NaOH thereto to maintainthe pH. In this case, the stirring power was maintained at the same asthat of the second process.

[Postprocess]

A postprocess was carried out by washing the reaction resultant anddrying the washed resultant in a hot-air dryer at about 150° C. for 24hours to obtain a nickel-based active material precursor.

Subsequently, the nickel-based active material precursor and LiOH wereheat-treated in a molar ratio of 1:1 under the following conditions.

A first heat treatment was performed in an air atmosphere at about 800°C. for 6 hours. A second heat treatment was performed by heat-treating aproduct of the first heat treatment in an oxygen atmosphere at about850° C. for 6 hours to obtain a nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂).

EXAMPLES 2 AND 3

Nickel-based active material precursors were prepared and nickel-basedactive materials were obtained therefrom in the same manner as inExample 1, except that the manufacturing process was changed such thatthe core, the intermediate layer, and the shell have porositycharacteristics as shown in Table 4 below.

COMPARATIVE EXAMPLE 1

A nickel-based active material precursor (Ni_(0.48)Co_(0.26)Mn_(0.36)OH)was synthesized according to a co-precipitation method described below.As a metal raw material forming the nickel-based active materialprecursor in the following manufacturing process, nickel sulfate, cobaltsulfate, and manganese sulfate were used.

[First process: 250 rpm, 0.50 M of NH₃, and pH of 11.40 to 11.60]

First, ammonia water having a concentration of 0.50 mol/L was added to areactor. After initiating reaction at a stirring speed of 250 kW/m³ anda reaction temperature of 50° C., the metal raw material and ammoniawater were added thereto at 6.0 ml/min and at 1.35 ml/min, respectively.Subsequently, NaOH was added thereto to maintain the pH. In this case,the pH of the reactor was in a range of 11.4 to 11.60. Within the pHrange, the reaction was performed for 33 hours.

A postprocess was carried out by washing the reaction resultant anddrying the washed resultant in a hot-air dryer at about 150° C. for 24hours to obtain a nickel-based active material precursor.

Subsequently, the nickel-based active material precursor and LiOH wereheat-treated in a molar ratio of 1:1 under the following conditions.

A first heat treatment was performed in an air atmosphere at about 800°C. for 6 hours. A second heat treatment was performed by heat-treating aproduct of the first heat treatment in an oxygen atmosphere at about850° C. for 6 hours to obtain a nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂).

COMPARATIVE EXAMPLE 2 Preparation of Nickel-based Active MaterialPrecursor

A nickel-based active material precursor was prepared and a nickel-basedactive material was prepared therefrom in the same manner as in Example1, except that the stirring power of the second process and the thirdprocess was 1.5 kW/m², the stirring power of the first process was 1.0kW/m², and the concentrations of ammonia water were gradually reduced inthe order of the first process, the second process, and the thirdprocess.

It was difficult to obtain the nickel-based active material precursorhaving a structure in which porosity gradually decreases in the order ofthe core, the intermediate layer, and the shell according to ComparativeExample 2.

PREPARATION EXAMPLE 1 Coin Half Cell

A coin half cell was prepared according to the following method by usingsecondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) obtained according to Example 1 as acathode active material.

96 g of the secondary particles of the nickel-based active material(LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂) obtained according to Example 1, 2 g ofpolyvinylidene fluoride, 47 g of N-methyl pyrrolidone as a solvent, and2 g of carbon black as a conductive agent were mixed using a mixer whileremoving air bubbles therefrom to prepare an uniformly dispersed cathodeactive material layer-forming slurry.

The slurry prepared according to the process was coated on an aluminumfoil by using a doctor blade to form a thin electrode plate. Theelectrode plate was dried at 135° C. for 3 hours or more, followed byrolling and vacuum drying to prepare a cathode.

A 2032 type coin half cell (coin cell) was prepared by using the cathodeand a lithium metal as a counter electrode. A separator (thickness:about 16 μm) formed of a porous polyethylene (PE) film was interposedbetween the cathode and the lithium metal counter electrode and anelectrolyte was injected thereinto, thereby preparing a 2032 type coinhalf cell.

In this regard, 1.1 M of a LiPF₆ solution prepared by dissolving LiPF₆in a mixed solvent including ethylene carbonate (EC) and ethylmethylcarbonate (EMC) in a volume ratio of 3:5 was used as the electrolyte.

PREPARATION EXAMPLES 2 and 3 Preparation of Coin Half Cell

Coin half cells were prepared in the same manner as in PreparationExample 1, except that the nickel-based active materials respectivelyprepared according to Examples 2 and 3 were used instead of thenickel-based active material prepared according to Example 1.

COMPARATIVE MANUFACTURE EXAMPLES 1 and 2 Preparation of Coin Half Cell

Lithium secondary batteries were prepared in the same manner as inPreparation Example 1, except that the nickel-based active materialsrespectively prepared according to Comparative Examples 1 and 2 wereused instead of the nickel-based active material prepared according toExample 1.

EVALUATION EXAMPLE 1 Particle Size Analysis

Particle sizes of the nickel-based active material precursor preparedaccording to Example 1 and Comparative Example 1 were analyzed. Particlesize analysis results are shown in Table 1 below. In Table 1, D10, D50,and D90 respectively refer to cumulative particle diameters at 10%, 50%,and 90% of a total cumulative particle diameter distribution ofparticles from the smallest particle diameter.

TABLE 1 Example D10 D50 D90 Example 1 8.61 11.57 14.90 ComparativeExample 1 10.35 11.99 13.70

EVALUATION EXAMPLE 2 Specific Surface Area and Composition Analysis

Compositions and specific surface areas of the nickel-based activematerial precursors prepared according to Example 1 and ComparativeExample 1 were analyzed and shown in Table 2 below. The compositionswere analyzed by Inductively Coupled Plasma (ICP) analysis and thespecific surface areas were evaluated by using a Brunauer, Emmett andTeller (BET) method.

In Table 2 below, particle sizes after 1 hour of reaction may bequantified by measuring a layer of the nickel-based active materialprecursor in which pores are formed. Scanning electron microscope (SEM)images of cross-sections may be used therefor.

TABLE 2 Comparative Item Example 1 Example 1 Composition ratio Ni 60.62060.7 Co 19.870 19.7 Mn 19.510 19.6 Transition metal (wt %) 64.4 64.6Particle size after 1 hour of reaction (μm) 6.53 2.26 Specific surfacearea(m²/g) 7.50 2.43

Referring to Table 2, the composition of the nickel-based activematerial precursor according to Example 1 was identified. In addition,the particle size of the nickel-based active material precursoraccording to Example 1 was increased when compared with that ofComparative Example 1 after 1 hour of reaction. Also, the nickel-basedactive material precursor according to Example 1 was an increasedspecific surface area when compared with that of Comparative Example 1.Thus, lithium secondary batteries having increased efficiency andcapacity may be manufacturing by using the nickel-based active materialprecursor according to Example 1.

EVALUATION EXAMPLE 3 X-Ray Diffraction (XRD) Analysis

Crystal structures of the nickel-based active material precursorsprepared according to Example 1 and Comparative Example 1 were analyzedby X-ray diffraction (XRD). The XRD was performed by using an X'pert pro(PANalytical) with Cu Kα radiation (1.54056 Å).

XRD analysis results are shown in Table 3 below and it may be confirmedthat the crystal plane (001) is well developed in Example 1.

TABLE 3 Comparative Item Example 1 Example 1 FWHM of peak correspondingto 0.728 0.506 crystal plane (001) (°) FWHM of peak corresponding to0.534 0.489 crystal plane (100) (°) FWHM of crystal plane (102) (°)1.690 1.380 a (Å) 3.024 3.042 c (Å) 4.608 4.590 c/a 1.518 1.506

Referring to Table 3, it was confirmed that the crystal plane (001) waswell developed in the nickel-based active material precursor accordingto Example 1 because a full width at half maximum (FWHM) of a (001) peakwas 0.7 or greater when compared with the nickel-based active materialprecursor according to Comparative Example 1.

EVALUATION EXAMPLE 4 SEM Analysis

Surfaces and cross-sections of particles of the nickel-based activematerial precursor prepared according to Example 1 and particles of thenickel-based active material precursor prepared according to ComparativeExample 1 were analyzed using a scanning electron microscope (SEM). AMagellan 400L (FEI company) was used as the scanning electronmicroscope. Cross-sections of samples were preprocessed by milling usinga CP2 manufactured by JEOL at 6 kV and 150 μA for 4 hours. In addition,the SEM analysis was performed at 350 V.

As a result of SEM analysis on the surfaces of the nickel-based activematerial precursors, primary particles are well oriented and pores arewell developed between the primary particles in the nickel-based activematerial precursor of Example 1, and thus a structure effective forintercalation and deintercalation of lithium may be formed after heattreatment in the preparation of the nickel-based active material.

In addition, as a result of SEM analysis on the cross-sections of thenickel-based active material precursors, the nickel-based activematerial precursor according to Comparative Example 1 has a structure inwhich the core had no pore. On the contrary, the nickel-based activematerial precursor according to Example 1 has a structure in which aporous core is formed and pores are also distributed with a gradient inthe shell as well as the core.

EVALUATION EXAMPLE 5 Porosity Analysis

SEM analysis was also carried out on the particles of the nickel-basedactive material precursors prepared according to Examples 1 to 3 andComparative Examples 1 and 2. A Magellan 400L (FEI company) was used asthe scanning electron microscope. Cross-sections of samples werepreprocessed by milling using a CP2 manufactured by JEOL at 6 kV and 150μA for 4 hours. In addition, the SEM analysis was performed at 350 V.

The analysis results are shown in Table 4 below. In Table 4 below, theporosity refers to a ratio of an area occupied by pores to a total area.

TABLE 4 Exam- Exam- Exam- Comparative Item ple 1 ple 2 ple 3 Example 1Porosity of core (%) 18.5 15.0 20.2 1.6 Porosity of intermediate 12.510.1 14.5 2.4 layer (%) Porosity of shell (%) 1.7 2.1 1.2 3.3

Referring to Table 4, it was confirmed that particles of thenickel-based active material precursor prepared according to Example 1had a porous structure in which the core had a higher porosity than thatof the shell and pores were developed.

On the contrary, the nickel-based active material precursor obtainedaccording to Comparative Example 1 did not have a structure includingthe core, the intermediate layer, and the shell which was shown in thenickel-based active material precursor according to Example 1. Inaddition, the nickel-based active material precursor obtained accordingto Comparative Example 2 did not have porosity gradually decreasing inthe order of the core, the intermediate layer, and the shell which is acharacteristic according to Example 1.

EVALUATION EXAMPLE 7 Surface Analysis using SEM

The nickel-based active material precursor prepared according to Example1 was analyzed using a scanning electron microscope. Based on the SEManalysis results, it was confirmed that the shape of primary particlesof the nickel-based active material precursor according to Example 1 wasan arrangement of plate particles.

EVALUATION EXAMPLE 8 High Temperature Lifespan

High temperature lifespans of the coin half cells prepared according toManufacture Examples 1 and 2 and Comparative Example 1 were evaluatedaccording to the following method.

First, each of the coin half cells was charged and discharged once with0.1 C for formation and then charged and discharged once with 0.2 C toidentify initial charging and discharging characteristics. Whilerepeating the charge/discharge process 50 times at 45° C. with 1 C,cycle characteristics were examined. The charge process was set to beginin a constant current (CC) mode, be converted into a constant voltage(CV) mode, and be cut off at 4.3 V with 0.05 C, and the dischargeprocess was set to be cut off in a CC mode at 3.0 V.

Changes in discharge capacity according to repeated cycles are shown inTable 7 below. In addition, FIGS. 3 and 4 are SEM images ofcross-sections of cathodes of the coin half cells according to Example 1and Comparative Example 1, respectively, after evaluation of lifespancharacteristics at high temperature. It was confirmed that almost nocracks occurred according to Example 1, while many cracks occurredaccording to Comparative Example 1.

TABLE 6 Comparative Item Example 1 Example 2 Example 1 Lifespan (%) 98.098.5 97.3

Referring to this, it was confirmed that the coin half cells accordingto

Manufacture Examples 1 and 2 had excellent lifespan characteristics athigh temperature.

EVALUATION EXAMPLE 9 Charging and Discharging Characteristics (InitialEfficiency)

First, each of the coin half cells prepared according to ManufactureExamples 1 and 2 and Comparative Preparation Example 1 was charged anddischarged once with 0.1 C for formation and then charged and dischargedonce with 0.2 C to identify initial charging and dischargingcharacteristics. While repeating the charge/discharge process 50 timeswith 1 C, cycle characteristics were examined. The charge process wasset to begin in a constant current (CC) mode, be converted into aconstant voltage (CV) mode, and be cut off at 4.3 V with 0.05 C, and thedischarge process was set to be cut off in a CC mode at 3.0 V.

(1) Initial Charge/discharge Efficiency (I.C.E)

Measurement was performed according to Equation 1 below.

Initial charge/discharge efficiency [%]=[Discharge capacity at1^(st)cycle/Charge capacity at 1^(st)cycle]×100   Equation 1

Initial charge/discharge efficiencies of coin half cells according toExample 4 and Comparative Example 3 were evaluated and the results areshown in Table 7 below.

TABLE 7 Charge capacity Discharge capacity I.C.E Example (mAh/g) (mAh/g)(%) Preparation Example 1 193.2 183.8 95.13 Preparation Example 2 198.5189.9 95.66 Comparative Preparation 200.0 180.9 90.45 Example 1

Referring to Table 7, the coin half cells according to ManufactureExamples 1 and 2 had higher charge/discharge efficiencies than that ofComparative Preparation Example 1.

EVALUATION EXAMPLE 10 Charging and Discharging Characteristics (RatePerformance)

Each of the coin half cells prepared according to Manufacture Examples 1and 2 and Comparative Preparation Example 1 was charged under theconditions of a constant current (0.2 C) and a constant voltage (4.3 V,0.05 C cut-off), rested for 10 minutes, and discharged under theconditions of a constant current (0.2 C, 0.33 C, 0.5 C, 1 C, 2 C, or 3C) until the voltage reached 3.0 V. That is, high-rate dischargecharacteristics (rate capabilities) of each coin half cell wereevaluated periodically changing the discharge rate at 0.2 C, 0.33 C, 0.5C, 1 C, 2 C, or 3 C while the number of charging and discharging cyclesincreases. However, each cell was discharged at a rate of 0.1 C duringthe 1^(st) to 3^(rd) charging and discharging cycles. In this regard,the high-rate discharge characteristics are represented by Equation 2below.

High-rate Discharge Characteristics (%)=(Discharge capacity whendischarging cell at predetermined constant current rate)/(Dischargecapacity when discharging cell at 0.1 C rate)×100   Equation 2

The results of the high-rate discharge characteristics are shown inTable 8 below.

TABLE 8 0.2 C 0.5 C 1 C 2 C Preparation Example 1 182.7 178.1 173.4167.7 Preparation Example 2 187.3 182.9 177.1 170.0 ComparativePreparation 178.2 173.1 167.8 162.3 Example 1

Referring to Table 8, the coin half cells prepared according toManufacture Examples 1 and 2 had excellent high-rate dischargecharacteristics when compared with the coin half cell prepared accordingto Comparative Preparation Example 1.

EVALUATION EXAMPLE 11 SEM Analysis

The nickel-based active material precursors prepared according toExample 1 and Comparative Example 2 were partially broken andcross-sections thereof were evaluated by SEM analysis.

Referring to this, as a result of identifying a structure of across-section of the broken nickel-based active material precursoraccording to Example 1, it was confirmed that the primary particles hada plate structure.

While one or more exemplary embodiments have been described withreference to the manufacture examples and examples, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope as defined by the following claims.

1. A nickel-based active material precursor for a lithium secondarybattery, comprising a core, an intermediate layer located on the core,and a shell located on the intermediate layer, wherein porositygradually decreases in the order of the core, the intermediate layer,and the shell, and each of the intermediate layer and the shell has aradial arrangement structure.
 2. The nickel-based active materialprecursor of claim 1, wherein the core has a porosity of 15 to 20% and apore size of 150 nm to 1 μm.
 3. The nickel-based active materialprecursor of claim 1, wherein the shell has a porosity of 2% or less anda pore size of less than 150 nm.
 4. The nickel-based active materialprecursor of claim 1, wherein the intermediate layer has a porosity of10% to 15%.
 5. The nickel-based active material precursor of claim 1,wherein an average particle diameter of the nickel-based active materialprecursor is in a range of 9 to 14 μm.
 6. The nickel-based activematerial precursor of claim 1, wherein the nickel-based active materialprecursor comprises plate particles, and major axes of the plateparticles are arranged in a radial direction.
 7. The nickel-based activematerial precursor of claim 1, wherein the nickel-based active materialprecursor is a compound represented by Formula 1 below:Ni_(1-x-y-z)Co_(x)Mn_(y)M_(z)OH   Formula 1 wherein in Formula 1, M isan element selected from the group consisting of boron (B), magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium(V), chromium (Cr), iron (Fe), copper (Cu), zirconium (Zr), and aluminum(Al), and x≤(1-x-y-z), y≤(1-x-y-z), 0<x<1, 0≤y<1, and 0≤z<1 aresatisfied.
 8. The nickel-based active material precursor of claim 7,wherein an amount of nickel contained in the nickel-based activematerial precursor is in a range of 0.33 to 0.95 mol % based on a totalamount of transition metals (Ni, Co, and Mn) and is higher than anamount of each of manganese and cobalt contained in the nickel-basedactive material precursor.
 9. The nickel-based active material precursorof claim 1, wherein the nickel-based active material precursor isNi_(0.6)Co_(0.2)Mn_(0.2)(OH)₂, Ni_(0.5)Co_(0.2)Mn_(0.3)(OH)₂,Ni_(0.33)Co_(0.33)Mn_(0.33)(OH)₂, Ni_(0.8)Co_(0.1)Mn_(0.1)(OH)₂, orNi_(0.85)Co_(0.1)Al_(0.05)(OH)₂.
 10. A method of producing anickel-based active material precursor for a lithium secondary battery,the method comprising: a first process of forming a core of thenickel-based active material precursor by reacting a complexing agent, apH regulator, and a metal raw material for forming the nickel-basedactive material precursor; a second process of forming an intermediatelayer on the core obtained in the first process; and a third process offorming a shell on the intermediate layer obtained in the secondprocess, wherein stirring powers of the second process and the thirdprocess are lower than that of the first process.
 11. The method ofclaim 10, wherein pH levels of reaction mixtures of the respective firstprocess, the second process, and the third process are the same.
 12. Themethod of claim 10, wherein concentrations of the complexing agentgradually increase in the order of the first process, the secondprocess, and the third process.
 13. A nickel-based active material for alithium secondary battery obtained from the nickel-based active materialprecursor for a lithium secondary battery according to claim
 1. 14. Alithium secondary battery comprising a cathode including thenickel-based active material for a lithium secondary battery of claim13, an anode, and an electrolyte interposed between the cathode and theanode.